The best optical illusions are often the ones we happen upon unintentionally, which is exactly what happened when redditor Liammm decided that water circling the drain of his sink would make for a nice photographic subject.

The illusion is even more pronounced when you're looking at a thumbnail of the image (try navigating to another post and looking at the photo in the sidebar); but full-resolution or not, the photo is easily one of the best examples of pareidolia we've ever seen:

Basically, we humans have this niggling habit of extracting what we believe to be significant information from patently insignificant stimuli. It's where we get Jesus-toast, and why we find familiar objects in shapeshifting cumulus. [In short], our brains are wired-up in such a way that we often see things that aren't really there.

Read more about the psychology and neuroanatomy of pareidolia, along with some of the latest research on the phenomenon, here.